The present invention relates generally to methods and devices for stabilizing the spine. More specifically, the invention provides methods and devices for fusing adjacent vertebrae and for localizing spinal bone growth.
Back pain affects millions of individuals and is a common cause of disability for the middle-aged working population. A frequent cause of back pain is rupture or degeneration of intervertebral discs.
Intervertebral discs, located between the endplates of adjacent vertebrae, stabilize the spine, distribute forces between vertebrae and cushion vertebral bodies. An intervertebral disc includes the nucleus pulposus, a gelatinous component that is surrounded and confined by an outer, fibrous ring, called the annulus fibrosus. In a healthy, undamaged spine, the annulus fibrosus prevents the nucleus pulposus from protruding outside the disc space.
Spinal discs may be displaced or damaged due to trauma, disease, or aging. Disruption of the annulus fibrosus allows the nucleus pulposus to protrude into the vertebral canal; a condition commonly referred to as a herniated or ruptured disc. The extruded nucleus pulposus may press on a spinal nerve, which may result in nerve damage, pain, numbness, muscle weakness and paralysis. Intervertebral discs may also deteriorate due to the normal aging process or disease. As a disc dehydrates and hardens, the disc space height will be reduced leading to instability of the spine, decreased mobility and pain.
In many instances, the only relief from the symptoms of these conditions is a discectomy, or surgical removal of all or a portion of an intervertebral disc followed by fusion of the adjacent vertebrae. The removal of the damaged or unhealthy disc will allow the disc space to collapse. Collapse of the disc space can cause instability of the spine, abnormal joint mechanics, premature development of arthritis or nerve damage, in addition to severe pain. Pain relief afforded by a discectomy and arthrodesis requires preservation of the disc space and eventual fusion of the affected motion segments.
One solution to the stabilization of an excised disc space is to fuse the vertebrae between their respective endplates. Typically an osteoinductive material is implanted at the treatment site to promote spinal fusion. Success of the discectomy and fusion procedure requires development of a contiguous growth of bone to create a solid mass capable of withstanding the compressive loads on the spine for the life of the patient.
Additionally, several metal spacers have been developed for implantation into a disc space and can be used to promote fusion. Medtronic Sofamor Danek, Inc., (Memphis, Tenn.) markets a number of hollow spinal cages, and a wide variety of other such cages are known in the art. For example, U.S. Pat. Nos. 5,015,247 and 5,984,967 to Michelson et al. and Zdeblick et al., respectively, disclose threaded spinal cages. The cages are hollow and can be filled with osteoinductive material, such as autograft, allograft and/or material isolated from the grafts. Apertures defined in the cages communicate with the hollow interior to provide a path for tissue growth between the vertebral endplates.
Such implants have been positioned in vivo by medical procedures well known in the art, including anterior and posterior approaches. In certain instances, it is possible that the osteoinductive material that includes an osteoinductive factor may diffuse, or otherwise migrate, from the implant into undesired locations, which may result in bone formation in these locations. For example, the osteoinductive material may diffuse out of the cage, or other implant, and may form bone inside an adjacent hematoma, or tissue, such as fibrous scar tissue. The can be an increased risk of hematoma formation with posterior lumbar interbody fusion (PLIF) or transforaminal lumbar interbody fusion procedure, because the blood released during these procedures can pool in the spinal canal or foramen space. Scar tissue formation from pooling blood from prior surgeries is also more prone in revision PLIF or TLIF procedures. There is therefore a need for methods for fusing adjacent vertebrae and osteoinductive compositions that aid in reducing formation of bone tissue in unwanted, or otherwise undesired, locations.
In light of the above described problems, there is a continuing need for advancements in the relevant field, including improved methods for treating orthopedic injuries and defects, osteogenic compositions and devices relating to enhancing spinal fusion. The present invention is such an advancement and provides a wide variety of benefits and advantages.